Rotational correlation of intravascular ultrasound image with guide catheter position

ABSTRACT

Apparatus and method are described for introducing an imaging catheter to the coronary vasculature. A guiding catheter is introduced so that the distal end of the guiding catheter engages a coronary os. The distal end of the guiding catheter is shaped so that a mark on the distal end is oriented in a predetermined orientation relative to the coronary vasculature. An imaging catheter is then introduced through the guiding catheter and an image of the mark is produced with the imaging catheter while in the guiding catheter. In this manner, the relative orientation of the produced image and the coronary vasculature is known.

This is a Continuation of application Ser. No. 08/470,673 filed Jun. 6,1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of ultrasonicimaging and therapeutic treatment of the vascular anatomy, andparticularly for the construction and use of guiding catheters used inaccessing the vascular anatomy. More particularly, the invention relatesto the rotational correlation of intravascular ultrasonic imagesproduced within such guiding catheters with the vascular orientation ofthe guiding catheters.

Arteriosclerosis, also known as atherosclerosis, is a common humanailment arising from the deposition of fatty-like substances, referredto as atheroma or plaque, on the walls of blood vessels. Such depositsoccur both in peripheral blood vessels that feed the limbs of the bodyand coronary blood vessels that feed the heart. When deposits accumulatein localized regions of the blood vessels, blood flow is restricted andthe person's health is at serious risk.

Numerous approaches for reducing and removing such vascular depositshave been proposed, including balloon angioplasty, where aballoon-tipped catheter is used to dilate a stenosed region within theblood vessel; placement of a stent for maintaining vessel patency afterangioplasty; atherectomy, where a blade or other cutting element is usedto sever and remove the stenotic material; and laser angioplasty, wherelaser energy is used to ablate at least a portion of the stenoticmaterial.

In order to more effectively introduce such interventional devices intothe vascular anatomy, and particularly into the coronary vasculature, aguiding catheter is generally employed. The guiding catheter is insertedpercutaneously into the patient's arterial system, usually by apercutaneous puncture made in the femoral artery in the groin. With theaid of a guidewire (and usually with the assistance of fluoroscopy), theguiding catheter is advanced upwardly through the patient's aorta to thecoronary ostia. Usually, the distal end of the guiding catheter isspecially shaped to facilitate placement of the distal tip of theguiding catheter against the ostium of one of the coronary arteries andto maintain the guiding catheter in place throughout the procedure. Theshape of the distal end allows the distal end of the guiding catheter topoint into the ostium, with the catheter body being buttressed againstthe opposite wall of the aorta.

Once the guiding catheter is in place, therapy proceeds by introducing atherapeutic catheter or other interventional device through the guidingcatheter and to the desired treatment location within the coronaryarteries. Before employing the therapeutic catheter, however, it isoften necessary to properly locate the diseased region of the vessel aswell as the position (including the orientation) of the therapeuticcatheter relative to the diseased region so that the interventionalelement on the therapeutic catheter can be employed to treat thediseased region. Directional devices, such as directional atherectomycatheters can be "aimed" at the disease to selectively remove tissue.One approach for visualizing the interior of the vessel is byintravascular ultrasound (IVUS) where a catheter having an ultrasonicimaging element is introduced beyond the guiding catheter and into thevessel to produce cross-sectional images of the vessel. Ultrasonicimaging catheters may also include an interventional element so thattherapy can occur without exchanging the imaging catheter for aninterventional catheter after imaging has occurred. For example, in thecase of atherectomy procedures, one common approach is to employ animaging catheter having a cutting element located inside of acanoe-shaped housing. On the backside of the housing is a low pressureballoon which is inflated to force the atherosclerotic tissue into theopening of the housing and into the path of the cutter for subsequentremoval. Often, the atherosclerotic buildup is only on one side of thevessel wall, commonly referred to as eccentric plaque, thereby making itdesirable to position the housing so that the cutting blade is directedonly against the eccentric plaque and not the healthy vessel wall. Oneproposed method for positioning the cutting blade is to rotate theproximal portion of the catheter (which is outside of the patient) untilthe opening in the housing is aimed at the diseased portion of thevessel. The balloon is then inflated and the cutter is advanced withinthe housing to shave away the atherosclerotic tissue.

While such ultrasonic images of the vessel assist in locating theexistence of the plaque, it has heretofore been difficult to preciselycorrelate the orientation of the cross-sectional images produced by theimaging catheter with the actual spatial orientation of the imagefeature within the blood vessel. Many imaging catheter constructionsprovide no information at all relative to the rotational orientation ofthe imaging catheter within the blood vessel while the image is beingproduced. In such cases, correlation of the image with the actualorientation of the blood vessel is difficult or impossible.

It would therefore be desirable to provide improved catheters andmethods which would facilitate correlation of an ultrasoniccross-sectional image with the physical orientation of the catheterproducing such an image within the coronary vasculature. In this way,regions of the blood vessel requiring therapy can be precisely locatedand targeted for subsequent interventional treatment. Further, it wouldbe particularly desirable if the rotational orientation of the imagingcatheter could be uniquely determined while within the guiding catheterso that the orientation of the imaging catheter can be correlated withthe real time ultrasonic image being produced. Most preferably, suchimprovements should require only modifications of proven catheterdesigns so that the other functions of the catheters are subsequentlyundisturbed.

2. Description of the Background Art

A variety of patents describe vascular guiding catheters, including U.S.Pat. Nos. 4,817,613; 5,163,921; and 5,318,032.

U.S. Pat. No. 5,054,492 describes an ultrasonic imaging catheter havingboth an ultrasonically opaque element and a fluoroscopic marker on thecatheter body. Both markers are employed to determine the actualrotational orientation of the catheter within the body lumen beingviewed.

SUMMARY OF THE INVENTION

The invention provides a method for introducing an imaging catheter tothe coronary vasculature. According to the method, a guiding catheter isintroduced so that a distal end of the guiding catheter engages acoronary ostium. The distal end of the guiding catheter is shaped sothat a mark on the distal end is oriented in a predetermined orientationrelative to the coronary vasculature. An imaging catheter is thenintroduced through the guiding catheter and is employed to produce animage of the mark while within the guiding catheter. In this way, animage of the mark is produced while the mark is in a known position sothat the orientation of the ultrasonic image relative to the actualspatial orientation of the guiding catheter (and to the coronaryvasculature) can be correlated.

In one aspect of the method, a screen is employed to produce the imageof the mark. The produced image is then rotated until in a preferredorientation relative to the coronary vasculature. Preferably, theorientation of the produced image is aligned with the predeterminedorientation of the mark. In this manner, the image displayed on thescreen is displayed with the same spatial orientation as both theimaging catheter and the guiding catheter within the coronaryvasculature.

In another aspect of the method, the imaging catheter is advanced beyondthe guiding catheter and into the coronary vasculature where the imagingcatheter is employed to visualize the features of the vessel wall. Theactual position of such observed features is then determined based onthe orientation of the imaging catheter relative to the coronaryvasculature as determined while in the guiding catheter. In this way, aphysician can estimate the actual position of the features observedwithin the vessel based on the produced image while in the guidingcatheter. After determining the actual position of the featuresobserved, a diseased region in the coronary vasculature istherapeutically treated.

In an exemplary aspect, the produced image is a cross-sectional image ofthe mark along with a cross-sectional image of the guiding catheter andthe surrounding coronary vasculature. The mark is preferablyultrasonically opaque, and the cross-sectional images of the mark, theguiding catheter, and the coronary vasculature are produced by sweepingan ultrasonic signal in the guiding catheter. In one particular aspect,the mark is a hole in the guiding catheter which appears as a void inthe cross-sectional image of the guiding catheter. Alternatively, themark can be formed as a thin strip of an ultrasonically opaque materialon or in the guiding catheter, with the cross-sectional image of themark appearing as a void or a shadow in the cross-sectional image of thesurrounding coronary vasculature.

The invention further provides an improved guiding catheter of the typehaving an elongate tube with a proximal end, a distal end, a lumenextending between the proximal and distal ends, and a shaped distal tip.Such a guiding catheter is improved by providing an ultrasonicallyvisible mark near the distal end, with the mark being in a uniqueposition relative to the shaped distal tip. In one aspect, the mark isformed as a hole in the catheter body. In another aspect, the mark is anultrasonically opaque material that is secured on or in the elongatetube, and is preferably formed as a thin strip.

The invention provides a catheter system for treatment of the coronaryvasculature. The catheter system includes a guiding catheter having anelongate tube with a proximal end, a distal end, a lumen extendingbetween the proximal and distal ends, and a shaped distal tip. Theguiding catheter further includes an ultrasonically visible mark formednear the distal end, with the mark being in a unique position relativeto the shaped distal tip. The system further includes an imagingcatheter that is translatable through the lumen of the guiding catheter.The imaging catheter includes an imaging element for ultrasonicallyvisualizing the mark and the surrounding coronary vasculature when inthe lumen.

In one aspect of the system, a screen is provided and is in electricalcommunication with the imaging catheter. With the screen, across-sectional image of the mark and the surrounding coronaryvasculature can be produced. In another aspect, a means are provided foradjusting the orientation of the produced visual image on the screen sothat the produced image is in a preferred orientation relative to thecoronary vasculature. Preferably, the preferred orientation is alignedwith the actual orientation of the distal end of the guiding catheter inthe coronary vasculature.

In another aspect of the system, the mark is a hole in the catheterbody. Alternatively, the mark includes an ultrasonically opaque materialsecured on or in the elongate tube.

In still a further aspect, the imaging element includes a rotatableultrasonic transducer for producing a cross-sectional image of the markand the surrounding coronary vasculature. Alternatively, a phased arraysystem may be employed to produce the cross-sectional image of the markand the surrounding coronary vasculature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an exemplary guiding catheter according to thepresent invention.

FIG. 2 is a more detailed view of a distal end of the catheter of FIG. 1showing a hole formed in the catheter body.

FIG. 3 illustrates an alternative embodiment of the distal end of thecatheter of FIG. 1 having a strip of ultrasonically opaque materialthereon.

FIG. 4 illustrates placement of the guiding catheter of FIG. 3 with thedistal end engaging a coronary ostium according to the presentinvention.

FIG. 5 is an enlarged view of the distal end of guiding catheter of FIG.3 within the coronary ostium.

FIGS. 6A-6F illustrate the ultrasonic images which would appear on amonitor screen when an ultrasonic imaging catheter is at each of therotational orientations illustrated by lines A--A through F--F in FIG.5.

FIG. 7 illustrates the ultrasonic image of FIG. 6B without rotation ofthe image to a preferred orientation on the screen.

FIG. 8 illustrates a method for therapeutically treating a stenoticregion in the coronary vasculature employing a catheter having a cuttingelement that is introduced through the guiding catheter of FIG. 3.

FIG. 8A illustrates the ultrasonic image which would appear on a monitorscreen at line A--A of FIG. 8 after the stenotic material has beenpartially removed and after the cutting catheter of FIG. 8 has beenwithdrawn.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Guiding catheters constructed in accordance with the principles of thepresent invention comprise an elongate tube having a proximal end, adistal end, and a lumen extending therebetween. The guiding catheterfurther includes a shaped distal tip, such as a bend or a curve in thetube, to facilitate placement of the distal end of the guiding catheterin a coronary ostium. As is known in the art, the distal tip can beshaped to accommodate the particular anatomy of the patient. In thisway, the guiding catheter can predictably and repeatedly be orientatedin a known position within the coronary ostium. The tip of the guidingcatheter includes a superior (pointing up) side and an inferior(pointing down) side. When appropriately positioned, the top of theguiding catheter tip is usually always positioned superior in the ostiumof the coronary artery, resulting in the superior side of the guidingcatheter being oriented at the top of a fluoroscopic image. In this way,the orientation of the distal end of the guiding catheter is in a knownposition relative to the patient's vascular anatomy.

The tube of the guiding catheter may be composed of a wide variety ofbiologically compatible materials, typically being made from natural orsynthetic polymers, such as silicone, rubber, natural rubber,polyethylene, polyvinylchloride, polyurethanes, polyesters,polytetrafluoroethylenes (PTFE) and the like. Particular techniques forforming the guiding catheters of the present invention are well knownand are described in the patent and medical literature.

The overall dimensions of the guiding catheter will depend on use, withthe length of the catheters varying widely, typically between about 50cm and 150 cm, usually being about 100 cm. The diameter of the tube mayalso vary widely, with the diameter typically being about 1 mm to 4 mm.Near the distal end of the tube, i.e. usually within about 0 cm to 3 cmof the distal tip, is an ultrasonically visible mark. A wide variety ofultrasonically visible marks can be provided including a hole formed inthe tube, an ultrasonically opaque material secured on or in the tube(such as paint, a flat piece of metal ribbon, or other low profilematerial capable of reflecting acoustic energy), or other ultrasoundabsorbing material such as urethanes, silicone, epoxies, and the like.The mark is formed near the distal end in a unique position relative tothe shaped distal tip. In this manner, when the distal tip is in a knownposition relative to the vascular anatomy, the orientation of anultrasonic image produced within the distal tip of the guiding cathetercan be determined upon visualization of the mark. Preferred positionsfor forming the mark include the superior and the inferior sides of theguiding catheter tip. Since the superior side of the guiding cathetertip will usually always be positioned superior in the coronary ostium(and since the orientation of the mark relative to the tip is known) theorientation of any ultrasonic image having the mark can easily becorrelated with the orientation of the coronary vasculature. In theevent that the ultrasonic image having the mark is not aligned with thefluoroscopic image of the coronary vasculature, the image of the markcan simply be rotated to align the image of the mark with thefluoroscopic image of the coronary vasculature.

To produce the image of the ultrasonically visible mark, an ultrasonicimaging catheter is employed. Such ultrasonic imaging catheters are wellknown in the art and usually employ an ultrasonic transducer mountedwithin a distal end of the catheter body and arrange to admit andreceive ultrasonic energy within an imaging plane disposed normal to theaxial direction of the catheter. Exemplary methods of intravascularultrasound are described in U.S. Pat. Nos. 4,794,931 and 5,000,185, thedisclosures of which are herein incorporated by reference. Such methodsinclude the mechanical rotation of the ultrasonic image transducer aboutthe imaging plane to produce a cross-sectional image of the imagingsite.

Before the therapeutic element is employed to treat a diseased region,the imaging element must be properly positioned at the treatment site.Positioning of the therapeutic element is accomplished by determiningthe orientation of the imaging catheter relative to the vascular anatomywhile within the guiding catheter as previously described. The imagingcatheter is then distally advanced beyond the distal tip of the guidingcatheter and toward the diseased region. As the imaging catheter isadvanced through the vessel, images are taken to locate the diseasedregion. The orientation of the resulting images are estimated based onthe orientation of the imaging catheter obtained while within theguiding catheter.

The images produced by the imaging catheter are cross-sectional imagesof the vascular anatomy. The images are preferably displayed on amonitor screen so that a physician can view the vascular anatomy whileperforming the procedure. When produced within the guiding catheter, theresulting images include cross-sectional views of the imaging catheterin addition to the vessel wall. When the marker at the distal tip of theguiding catheter comprises a hole in the catheter body, an ultrasonicimage of the mark will appear as a discontinuity in the image of thecatheter body at the position of the marker. In the event that anacoustically reflective strip of material is employed as the mark, ashadow will be produced in the ultrasonic image, where the position ofthe shadow corresponds to the position of the marker on the distal tipof the catheter body. In this manner, the physician viewing the image onthe monitor will be able to correlate the precise rotational orientationof the guiding catheter relative to the features which are revealed inthe image. For example, in the case where the marker is formed on thesuperior side of the catheter body, the resulting image on the screenshould have the shadow extending toward the top of the screen to havethe resulting image in the same orientation as the guiding catheterwithin the coronary vasculature. If the resulting image is notpositioned in such a manner, the invention provides for the rotation ofthe image on the screen so that it is aligned with the orientation ofthe guiding catheter within the coronary vasculature.

Referring now to FIGS. 1 and 2, an exemplary embodiment 10 of a guidingcatheter of the present invention will be described. The guidingcatheter 10 includes tubular flexible catheter body 12 having a proximalend 14 and a distal end 16. A proximal housing 18 having a hemostasisvalve is generally secured to the proximal end 14 of the catheter body12 and includes a side port 20 for injecting fluids, such as saline andcontrast media, into the guiding catheter 10. At the distal end 16 is ashaped distal tip 22. The distal tip 22 is shaped according to theparticular features of the patient's vascular anatomy in order tofacilitate predictable and repeatable placement of the distal end 16into a coronary ostium. At the distal tip 22 is a hole 24. As previouslydescribed, the hole 24 serves as an ultrasonic reference marker whichappears as a discontinuity in the image of the catheter body 12 whenviewed from within the guiding catheter 10 by an ultrasonic imagingcatheter.

An alternative embodiment of the distal tip 22 is shown in FIG. 3 andincludes a thin strip of acoustically reflective material 26 as theultrasonic reference marker. The strip 26 produces a shadow in theultrasonic image of the vascular anatomy produced by the imagingcatheter.

Referring back to FIG. 1, the marker 24 is shown on a superior side 28of the catheter body 12. In this way, when the guiding catheter 10 isintroduced into the coronary ostium, the hole 24 is located superior inthe coronary ostium. Alternatively, the hole 24 (or strip 26) can beformed at other unique positions at the distal tip 22, such as at aninferior side 30 of the catheter body 12. Since the distal tip 22 isfashioned to be received into the coronary ostium at a known andrepeatable position, unique positioning of the hole 24 on the distal tip22 provides for a known position of the hole 24 relative to the coronaryvasculature when the distal tip 22 is received in the coronary ostium.

Referring to FIG. 4, exemplary positioning of the guiding catheter 10(having the strip 26) will be described in greater detail. Initially, alarge guidewire (not shown) is introduced into the aorta 34. Usually,fluoroscopic imaging is employed to assist in the positioning of theguidewire. After the guidewire is placed over the aortic arch, theguiding catheter 10 is advanced over the guidewire until the distal tip22 is beyond the distal tip of the guidewire. As previously described,the shaped distal tip 22 allows the guiding catheter 10 to be receivedin the coronary ostium 36 at a known position. The physician will torqueand advance the guiding catheter 10 until it "pops" into the appropriatecoronary ostium 36. As illustrated in FIG. 4, the strip 26 is on thesuperior side 28 of the catheter body 12 and is received superior in thecoronary ostium 36. In this manner, both the catheter body 12 and thestrip 26 are in a known position relative to the coronary vasculature.

Once the guiding catheter 10 is in the desired position, a coronaryguidewire 32 is delivered into the coronary artery through the guidingcatheter 10. An imaging catheter 38 is then introduced through theguiding catheter 10, typically over the guidewire 32. The imagingcatheter 38 includes a cable 40 for rotating the ultrasonic transducer(not shown) in the catheter 38. Alternatively, a phased array cathetersystem can be employed to image the vessel walls.

Referring to FIGS. 5 and 6A-6F, ultrasonic imaging of coronaryvasculature will be described. FIGS. 6A-6F illustrate monitor imagesproduced by the imaging catheter 38 at lines A--A through F--F of FIG.5, respectively. As shown in FIG. 6A, the ultrasonic image producedwithin the guiding catheter 10 reveals the imaging catheter 38 and theguide catheter body 12. The cross-sectional image produced by theimaging catheter 38 when intersecting the strip 26 is shown in FIG. 6B.The resulting image reveals the imaging catheter 38 and the catheterbody 12. The image of the strip 26 appears as an acoustic vector 42extending from the image of the outside catheter wall (much like alighthouse beacon). As shown in FIG. 6B, the vector 42 extends towardthe top of the screen and is therefore aligned with the actualorientation of the strip 26 within the coronary ostium 36. Hence, aphysician viewing the screen of FIG. 6B would have a view of the distaltip 22 in the same spatial orientation as the distal tip 22 held withinthe coronary ostium 36. Usually, as illustrated in FIG. 7, the vector 42is not aligned with the actual orientation of the distal tip 22 withinthe coronary ostium 36. In such an event, the image on the screen canoptionally be rotated with a software program until the shadow 42 isaligned with the known position (in this case superior) of the strip 26and-distal tip 22 in the coronary ostium 36.

Referring to FIG. 6C, the image produced by the imaging catheter 38 whenadvanced distally beyond the distal end 16 of the catheter body 12 isshown. The image includes an image of the imaging catheter 38, theannular vessel wall 43 of the proximal coronary artery, which typicallyappears in three layer structure, and an annular ring of plaque 44 builtup on the interior walls of the proximal coronary artery. At positionD--D, an amount of eccentric plaque 46 exists in the coronary artery asshown in FIG. 6D. The eccentric plaque 46 is located inferior in thecoronary artery, opposite the 5 position of the strip 26 in the coronaryostium 36. Although the image of the strip 26 does not appear on theimage of FIG. 6D, the image of the strip 36 obtained while in theguiding catheter 10 is used to estimate the position of the eccentricplaque 46 within the coronary artery since the imaging catheter 38 isadvanced just distal, usually only 1 mm to 30 mm from the strip 26. Whenaxially advanced by such an amount, the distal tip 22 experiences littleor no rotation within the coronary artery, thereby insuring that theimage produced at position D--D is at substantially the same rotationalposition as the image attained at position B--B. The length of theeccentric plaque 46 is determined by producing images along the coronaryartery until the plaque 44 once again becomes annularly disposed aboutthe coronary artery as shown in FIG. 6E, or totally disappears as shownin FIG. 6F.

Referring to FIG. 8, therapeutic treatment of the coronary artery willbe described. After producing the image of FIG. 6B so that the relativeorientation of the imaging catheter 38 can be determined (and afteraligning the vector 42 with the actual orientation of the strip 26within the coronary ostium 36 if desired or needed), the imagingcatheter 38 is distally advanced beyond the distal end 16 of thecatheter body 12 to visualize the coronary artery. The imaging catheter38 is advanced through the coronary artery until reaching the plaque 46as shown in FIG. 6D. As the imaging catheter 38 is distally advancedtoward the plaque 46, the rotational orientation of the imaging catheter38 will usually remain virtually unchanged. Hence, the position of theimaging catheter 39 relative to the plaque 46 will be known. Based onthe image of the plaque 46 and the image produced as FIG. 6B, the actualorientation of the plaque 46 in the artery can be determined. Once theactual orientation of the plaque is known, the imaging catheter 38 iswithdrawn from the coronary artery and an atherectomy catheter 39 isintroduced over the guidewire.

The atherectomy catheter 39 includes a canoe-shaped housing 48 having anaperture 50 therein. Within the aperture 50 is a cutting element 52which is employed to shave the plaque 46 from the walls of the coronaryartery. A balloon 54 is provided on the housing 48 opposite the aperture50 for forcing the cutting element 52 against the plaque 46 wheninflated. When the area having the eccentric plaque 46 is reached underfluoroscopic guidance, the position of the cutter 52 on the atherectomycatheter 39 can be manipulated to ensure that it is facing the eccentricplaque 46, based on the known orientation of the plaque from theprevious ultrasound image. If the cutting element 52 is not adjacent theplaque 46, the atherectomy catheter 39 can be rotated from its proximalend (which is outside the patient) to adjust the rotational position ofthe cutting element 52. When at the proper location, the balloon 54 isinflated and the cutting element 52 is actuated to remove the plaque 46from the coronary artery. After removal of the plaque 46, imaging of thearea can again occur (as illustrated in FIG. 8A) to determine ifsufficient plaque 46 has been removed.

Although described in the context of the right coronary artery, theinvention can be used to image and therapeutic treat other areas of thevascular anatomy, such as the left coronary artery or other vessels. Themethods of the present invention are particularly useful in the rightcoronary artery because no branches or other land marks exist in theright coronary ostium to assist in the correlation of the ultrasonicimage to the angiographic image.

Although the foregoing invention has been described in some detail byway of illustration and example, for purposes of clarity ofunderstanding, it will be obvious that certain changes and modificationsmay be practiced within the scope of the appended claims.

What is claimed is:
 1. A method for introducing an imaging catheter to abody lumen, said method comprising:introducing a guiding catheter sothat a distal end of the guiding catheter is positioned at a preferredlocation within the body lumen, wherein said distal end is shaped sothat a mark on the distal end is disposed in predetermined orientationrelative to the body lumen; introducing an imaging catheter through theguiding catheter; and producing with the imaging catheter an image ofthe mark while in the guiding catheter, whereby the relative orientationof the produced image and the body lumen vasculature is known.
 2. Amethod as in claim 1, wherein the body lumen is within the coronaryvasculature, and wherein the preferred location is at a coronary ostium.3. A method as in claim 2, further comprising rotating the producedimage on a screen so that the produced image is in a preferredorientation relative to the coronary vasculature.
 4. A method as inclaim 3, wherein the preferred orientation of the produced image isaligned with the predetermined orientation of the mark.
 5. A method asin claim 2, further comprising advancing the imaging catheter into thecoronary vasculature, whereby the actual position of features observedcan be determined based on the relative orientation of the imagingcatheter and the coronary vasculature.
 6. A method as in claim 5,further comprising therapeutically treating a diseased region in thecoronary vasculature after advancing the imaging catheter into thecoronary vasculature and obtaining the image of the diseased region. 7.A method as in claim 2, wherein the produced image is a cross-sectionalimage of the mark, and further comprising producing with the imagingcatheter a cross-sectional image of the guiding catheter and thesurrounding coronary vasculature subsequent to producing the image ofthe mark.
 8. A method as in claim 7, wherein the mark is ultrasonicallyopaque, and wherein the cross-sectional images of the mark, the guidingcatheter, and the coronary vasculature are produced by sweeping anultrasonic signal in the guiding catheter.
 9. A method as in claim 8,wherein the sweeping step comprises mechanically rotating an ultrasonictransducer in the guiding catheter.
 10. A method as in claim 8, whereinthe sweeping step comprises providing the ultrasonic signal with aphased-array catheter system.
 11. A method as in claim 8, wherein themark is a hole in the guiding catheter, and wherein the cross-sectionalimage of the mark appears as a void in the cross-sectional image of theguiding catheter.
 12. A method as in claim 8, wherein the mark is formedas a thin strip on or in the guiding catheter, and wherein thecross-sectional image of the mark appears as a void in thecross-sectional image of the surrounding coronary vasculature.
 13. Aguiding catheter comprising:an elongate tube having a proximal end, adistal end, a lumen extending between said proximal and distal ends, anda shaped distal tip; an ultrasonically visible mark formed near thedistal end, wherein said tube includes a superior side and an inferiorside, and wherein said mark is located at a known position relative tothe shaped distal tip, wherein said distal tip is shaped such that saidmark will locate itself at a predetermined orientation relative to abody lumen when introduced into the body lumen.
 14. An improved guidingcatheter as in claim 13, wherein the mark comprises an ultrasonicallyopaque material secured on or in the elongate tube.
 15. An improvedguiding catheter as in claim 14, wherein the ultrasonically opaquematerial is formed as a thin strip on or in the tube.
 16. An improvedguiding catheter as in claim 13, wherein the distal end of the tube iscurved.
 17. An improved guiding catheter as in claim 13, wherein saidmark is located on the superior side, and wherein said distal tip isshaped such that said mark will locate itself superior in a coronaryostium when introduced into the coronary vasculature.
 18. An improvedguiding catheter as in claim 17, wherein said distal end is open suchthan an imaging catheter used to visualize the mark may be translatedthrough the lumen, out the distal end, and into a coronary artery tovisualize the artery.
 19. A catheter system for treatment of thecoronary vasculature, comprising:a guiding catheter having an elongatetube with a proximal end, a distal end, a lumen extending between saidproximal and distal ends, and a shaped distal tip, wherein the guidingcatheter further includes an ultrasonically visible mark formed near thedistal end, wherein said mark is in a known position relative to theshaped distal tip; and an imaging catheter translatable through thelumen of the guiding catheter, the imaging catheter having an imagingelement for ultrasonically visualizing the mark and the surroundingcoronary vasculature when in the lumen.
 20. The system of claim 19,further comprising a screen in electrical communication with the imagingcatheter for producing a visual cross-sectional image of the mark andthe surrounding coronary vasculature; andmeans for adjusting theorientation of the produced visual image on the screen so that theproduced image is in a preferred orientation relative to the coronaryvasculature.
 21. The system of claim 20, wherein the preferredorientation is aligned with the actual orientation of the distal end ofthe guiding catheter in the coronary vasculature.
 22. The system ofclaim 19, wherein the mark comprises an ultrasonically opaque materialsecured on or in the elongate tube.
 23. The system of claim 19, whereinthe imaging element comprises a rotatable ultrasonic transducer forproducing a cross-sectional image of the mark and the surroundingcoronary vasculature.
 24. The system of claim 19, wherein the imagingelement comprises a phased array transducer system for producing across-sectional image of the mark and the surrounding coronaryvasculature.
 25. The system of claim 19, further comprising anatherectomy catheter having a cutting element near a distal end forremoving plaque from the lumen following visualization with the imagingcatheter.